scholarly journals White-light speckle image correlation applied to large-strain material characterization

2009 ◽  
pp. 377-392
Author(s):  
Giovanni B. Broggiato ◽  
Luca Cortese
Keyword(s):  
Material Characterization ◽  
Plastic Material ◽  
Large Strain ◽  
Equivalent Stress ◽  
Tensile Tests ◽  
Equivalent Strain ◽  
Image Correlation ◽  
Plastic Behavior ◽  
Full Field ◽  
Measurement Devices

In experimental mechanics, the possibility of tracking on component surfaces the full-field stress and strain states during deformation can be utilized for many purposes such as formability limits determination, quantification of stress intensification factors, material characterization and so on. Concerning the last topic, an interesting application could be a direct identification of the elasto-plastic material response up to large deformation. It is well known, in fact, that with traditional measurement devices it is possible to retrieve the true equivalent stress versus true equivalent strain data from tensile tests only up to the onset of necking, where localization starts to occur. This work aims to show how from the knowledge of a tensile test full-field strain and of load data it will be possible to obtain the full-stress field as well as the complete material elasto-plastic behavior.

scholarly journals Identification of the Mechanical Properties of Superconducting Windings Using the Virtual Fields Method

2010 ◽  
Vol 24-25 ◽  
pp. 379-384
Author(s):  
J.H. Kim ◽  
F. Nunio ◽  
Fabrice Pierron ◽  
P. Vedrine
Keyword(s):  
Least Square Method ◽  
Numerical Differentiation ◽  
Tensile Tests ◽  
Least Square ◽  
Image Correlation ◽  
Stereo Image ◽  
Correlation Technique ◽  
Virtual Fields Method ◽  
Displacement Fields ◽  
Full Field

Tensile tests were performed in order to identify the stiffness components of superconducting windings in the shape of rings (also called ‘double pancakes’). The stereo image correlation technique was used for full-field displacement measurements. The strain components were then obtained from the measured displacement fields by numerical differentiation. Because differentiation is very sensitive to spatial noise, the displacement maps were fitted by polynomials before differentiation using a linear least-square method. Then, in the orthotropy basis, the four in-plane stiffnesses of the double pancake were determined using the Virtual Fields Method.

scholarly journals Robust Filtering Options for Higher-Order Strain Fields Generated by Digital Image Correlation

2020 ◽  
Vol 1 (4) ◽  
pp. 174-192
Author(s):  
Nedaa Amraish ◽  
Andreas Reisinger ◽  
Dieter H. Pahr
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Tensile Tests ◽  
Image Correlation ◽  
Field Strain ◽  
Strain Fields ◽  
Full Field ◽  
Low Pass ◽  
Discrete Measurement ◽  
Mean Filtering

Digital image correlation (DIC) systems have been used in many engineering fields to obtain surface full-field strain distribution. However, noise affects the accuracy and precision of the measurements due to many factors. The aim of this study was to find out how different filtering options; namely, simple mean filtering, Gaussian mean filtering and Gaussian low-pass filtering (LPF), reduce noise while maintaining the full-field information based on constant, linear and quadratic strain fields. Investigations are done in two steps. First, linear and quadratic strain fields with and without noise are simulated and projected to discrete measurement points which build up strain window sizes consisting of 6×5, 12×11, and 26×17 points. Optimal filter sizes are computed for each filter strategy, strain field type, and strain windows size, with minimal impairment of the signal information. Second, these filter sizes are used to filter full-field strain distributions of steel samples under tensile tests by using an ARAMIS DIC system to show their practical applicability. Results for the first part show that for a typical 12×11 strain window, simple mean filtering achieves an error reduction of 66–69%, Gaussian mean filtering of 72–75%, and Gaussian LPF of 66–69%. If optimized filters are used for DIC measurements on steel samples, the total strain error can be reduced from initial 240−300 μstrain to 100–150 μstrain. In conclusion, the noise-floor of DIC signals is considerable and the preferable filters were a simple mean with s*¯ = 2, a Gaussian mean with σ*¯ = 1.7, and a Gaussian LPF with D0*¯ = 2.5 in the examined cases.

Fatigue Crack Growth Rates and Tensile Strength of Titanium Produced by Means of Selective Laser Melting

2014 ◽  
Vol 627 ◽  
pp. 305-308 ◽  
Author(s):  
Tomasz Brynk ◽  
Barbara Romelczyk ◽  
Zbigniew Pakiela ◽  
Tomasz Kurzynowski ◽  
Edward Chlebus
Keyword(s):  
Mechanical Properties ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Selective Laser Melting ◽  
Pure Titanium ◽  
Tensile Tests ◽  
Image Correlation ◽  
Laser Melting ◽  
Full Field

Mini-samples technique was utilized to determine mechanical properties of technically pure titanium produced by means of selective laser melting (SLM). Full-field digital image correlation (DIC) measurements and inverse method were applied for crack tip position and stress intensity factors calculations in the case of fatigue crack growth rate tests. DIC was also used for strain measurement during tensile tests on sub sized samples. There was studied the influence of samples orientation on the mechanical properties of mini-samples. Samples were cut out from rectangular cubes and were oriented with 0°, 45° or 90° angle to the direction of laser beam travel. There were also tested samples directly produced via SLM. Additionally microstructure observations were performed to verify the quality of SLM processed materials and explain mechanical properties variations.

Buckling Measurement of Cylindrical Shells by Digital Image Correlation Method

2013 ◽  
Author(s):  
Tzu-Yu Kuo ◽  
Wei-Chung Wang ◽  
Chun-I Chu ◽  
Jia-He Chen ◽  
Te-Heng Hung ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Strain Measurement ◽  
Cylindrical Shells ◽  
Compressive Load ◽  
Correlation Method ◽  
Tensile Tests ◽  
Image Correlation ◽  
Strain Gages ◽  
Full Field

In this study, deformation of cylindrical shells under axial compressive load was studied and characterized by a noncontact detection technique, called digital image correlation (DIC). As opposed to commonly used strain gages for measuring structure strains at specific points, the DIC method can render not only 2D but also 3D full-field measurements for strain as well as structure deformation. The accuracy of strain measurement obtained using the DIC method was carefully validated by following ASTM standard E8 for strain measurement using strain gages in tensile tests. The DIC technique provided convenient measurements for characterizing the buckling behaviors of defective cylindrical shell samples. This study has engineering implications for providing 3D strain and deformation analyses to ensure structure reliability and safety.

A strain-based approach to study interaction between non-coplanar through-thickness edge notches

2018 ◽  
Vol 53 (8) ◽  
pp. 687-698 ◽  
Author(s):  
Kaveh Samadian ◽  
Stijn Hertelé ◽  
Wim De Waele
Keyword(s):  
Brittle Fracture ◽  
Failure Modes ◽  
Structural Integrity ◽  
Equivalent Strain ◽  
Image Correlation ◽  
Combination Rules ◽  
Full Field ◽  
Integrity Assessment ◽  
Double Edge ◽  
Fundamental Insight

Structural integrity assessment procedures to assess the effect of interaction between multiple adjacent flaws normally consist of two stages. First, alignment rules categorize non-coplanar flaws as aligned or non-aligned. Second, combination rules classify aligned flaws as interacting or non-interacting. Although these criteria are applied to different failure modes like brittle fracture, elastic–plastic fracture and plastic collapse, most of them were developed based on linear elastic fracture mechanics for the sake of simplicity. However, there are very limited references available for the technical background of these criteria. This lack of justifying backgrounds becomes more critical when applying these procedures to any other failure modes other than brittle fracture. This article studies the interaction between non-coplanar edge notches in scenarios of large deformation. Hereto, strain patterns are studied through full-field deformation measurements utilizing both experimental and numerical tools. Digital image correlation is used to measure strain during experiments and to verify the finite element analyses. The results show that in addition to the crack driving force, which represents a local response of notches, the global strain distribution within the specimen in terms of strain patterns can be used to probe the interaction between non-coplanar flaws. The authors suggest a novel criterion based on the trajectory of maximum equivalent strain to distinguish between aligned and non-aligned flaws. This study is based on double-edge notched tension specimens and gives a fundamental insight into flaw interaction in failure modes other than brittle fracture.

scholarly journals Failure Prediction for the Tearing of a Pin-Loaded Dual Phase Steel (DP980) Adjusting Guide

2019 ◽  
Vol 9 (24) ◽  
pp. 5460 ◽  
Author(s):  
Seokmoo Hong ◽  
Jinkyoo Kim ◽  
Taehwan Jun
Keyword(s):  
Large Strain ◽  
Damage Model ◽  
Failure Prediction ◽  
Strain Range ◽  
Complex Loading ◽  
Tensile Tests ◽  
Material Behavior ◽  
Image Correlation ◽  
Failure Behavior ◽  
Loading Mode

Owing to their outstanding strength, in recent years, there has been an increased use of advanced high-strength steel (AHSS) sheets in the automotive sector. Their low formability, however, poses a challenge to forming, and failure prediction requires accurate knowledge of its material behavior over a large strain range up to ultimate failure, in order to exploit their full capacity in forming, but also in crash events. For predicting the fracture of an adjusting guide loaded by a pin, first, the force–displacement data are extracted from tensile tests using DP980 specimens of diverse shapes, all of which represent a certain loading mode. Using digital image correlation (DIC), we determine the stress triaxialities corresponding to the diverse loading conditions and establish the triaxiality failure diagram (TFD), which serves as the basis for the generalized incremental stress state-dependent damage model (GISSMO). Then, the damage parameters (necking and failure strains) are determined for each loading mode by reverse engineering-based optimization. Finally, these damage parameters are applied to the adjusting guide, and the numerical results are compared with the experimental data. Comparisons of the external load–displacement curves and the local equivalent strain distributions show that using the damage model with the material parameters obtained in here allows for the accurate prediction of the guide’s failure behavior, and the applicability of GISSMO to complex loading cases.

Assessing wood quality by spatial variation of elastic properties within the stem: Case study of Pinus pinaster in the transverse plane

2014 ◽  
Vol 44 (2) ◽  
pp. 107-117 ◽  
Author(s):  
J. Pereira ◽  
J. Xavier ◽  
J. Morais ◽  
J. Lousada
Keyword(s):  
Elastic Properties ◽  
Pinus Pinaster ◽  
Growth Ring ◽  
Wood Quality ◽  
Tensile Tests ◽  
Image Correlation ◽  
Annual Growth ◽  
Full Field ◽  
Annual Growth Ring ◽  
Annual Growth Rings

The wood quality of maritime pine (Pinus pinaster Ait.) is discussed in view of spatial variability of density, annual growth ring characteristics, and transverse elastic properties within and among five basal logs. X-ray microdensitometry measurements are carried out to assess both average (Dmean) and local (DEW, DLW) densities of annual growth rings, as well as the respective dimensions (EWW, LWW) and fractions of earlywood (EW) and latewood (LW) layers. Mechanical tensile tests on a set of specimens with different ring orientation are proposed. Transverse elastic properties are determined by coupling an inverse identification strategy with full-field deformation measurements provided by digital image correlation. For a suitable range of off-axis angles, this method allows the simultaneous characterisation of the four orthotropic elastic properties in the RT plane: ER, ET, νRT, and GRT. These results are found in agreement with reference values. From the sampled specimens among logs, ER and GRT are robustly identified in all cases and therefore are selected for further analysis of structure-properties relationships. Correlations between Dmean and ER and GRT are positive and statistically significant. Furthermore, other parameters also show significant correlations with the elastic constants, especially Dmin, LWW, and DEW.

scholarly journals Strain Evolution Measurement at the Microscale of a Dual Phase Steel Using Digital Image Correlation

2010 ◽  
Vol 24-25 ◽  
pp. 201-206 ◽  
Author(s):  
H. Ghadbeigi ◽  
C. Pinna ◽  
Steven Celotto ◽  
J.R. Yates
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Dual Phase Steel ◽  
Tensile Tests ◽  
Image Correlation ◽  
Scanning Electron Micrographs ◽  
Plastic Strains ◽  
Full Field ◽  
Loading Direction

Digital Image Correlation (DIC) together with in-situ tensile testing has been used to measure in DP1000 steel the evolution of plastic strains at the microstructure scale. Interrupted tensile tests were performed on specially designed samples and scanning-electron micrographs were taken at regular applied strain intervals. Patterns defined by the microstructural features of the material have been used for the correlation carried out using LAVision software. The full field strain maps produced by DIC show a progressive localisation of deformation into bands at about 45o with respect to the loading direction. Plastic strains as high as 130% have been measured within the ferrite phase.

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